Chapter 7 Skeletal System PDF

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Lecture notes on the Skeletal System...

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Chapter 7: SKELETAL SYSTEM 7.1 Introduction - Bones, the organs of the skeletal system, support and protect softer tissues, provide points of attachment for muscles to enable body movement, house blood-producing cells, and store inorganic salts. 7.2 Bone Structure - Bone classification: - Bones may be classified according to their shape--long, short, flat, or irregular. - Parts of a Long Bone - At each end of a long bone is an expanded portion called an epiphysis, which articulates (forms a joint) with another bone. - The epiphysis that is nearest the attachment to the trunk of the body is called the proximal epiphysis. - The epiphysis that is farthest from the trunk of the body is called the distal epiphysis. - The shaft of the bone, between the epiphysis, is called the diaphysis. - The wall of the diaphysis is mainly composed of tightly packed tissue called compact bone, also called cortical bone. - Compact bone has a continuous extracellular matrix with no gaps. - The epiphyses, in contrast, are composed largely of spongy bone, also called cancellous bone, with thin layers of compact bone on their surfaces. - A tough covering of dense connective tissue called the periosteum, completely encloses the bone, except for the articular cartilage on the bone’s ends. - The periosteum is firmly attached to the bone, and periosteal fibers are continuous with the connecting ligaments and tendons. - The periosteum also helps form and repair bone tissue. - Compact bone in the diaphysis of a long bone forms a tube with a hollow chamber called the medullary cavity, that is continuous with the spaces of the spongy bone. - Microscopic Structure - Bone cells called osteocytes occupy very small, bony chambers called lacunae. - The lacunae are within the bony matrix of the lamellae, which form concentric circles around central canals (Haversian canals). - In compact bone, osteocytes and layers of extracellular matrix are clustered around a central canal and form a cylinder-shaped unit called an osteon (Haversian system). Many osteons together form the substance of compact bone. 7.4 Bone Function - Bones shape, support, and protect body structures. - Aid in body movements, house tissue that produces blood cells, and store inorganic salts. - Support, Protection, and Movement - Bones give shape to structures such as the head, face, thorax, and limbs. - They also support and protect. - For example, the bones of the lower limbs, pelvis, and backbone support the body’s weight.

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The bones of the skull protect the eyes, ears, and brain. Bones of the rib cage and shoulder girdle protects the heart and lungs, whereas the bones of the pelvic girdle protects the lower abdominal and internal reproductive organs. - Bones and muscles interact to cause limbs and other body parts to move. - Blood Cell Formation - The process of blood cell formation is called hematopoiesis. - Two types of marrow: red and yellow. - Red marrow functions in the formation of red blood cells, white blood cells, and blood platelets. - The color comes from the oxygen-carrying pigment hemoglobin in the red blood cells. - Yellow marrow, which stores fat, replaces much of the red marrow when someone ages. - Storage of Inorganic Salts - Vital metabolic processes require calcium. - Bones store calcium. - The extracellular matrix of bone tissue is rich in calcium salts, mostly in the form of calcium phosphate. 7.5 Skeletal Organization - Two major portions: an axial skeleton and the appendicular skeleton. - The axial skeleton consists of the bony and cartilaginous parts that support and protect the organs of the head, neck, and trunk. - Skull. The skull is composed of the cranium, or brain case, and the facial bones. - Vertebral Column. The vertebral column, or spinal column (backbone), consists of many vertebrae separated by cartilaginous intervertebral discs. Near the distal end of the vertebral column, five vertebrae fuse, forming the sacrum, which is part of the pelvis. The coccyx, a small, rudimentary tailbone composed of four fused vertebrae, is attached to the end of the sacrum. - Thoracic Cage. The thoracic cage protects the organs of the thoracic cavity and the upper abdominal cavity. It is composed of twelve pairs of ribs, which articulates posteriorly with the thoracic vertebrae. The thoracic cage also includes the sternum, or breastbone, to which most of the ribs attach anteriorly. - The appendicular skeleton consists of the bones of the upper and lower limbs and the bones that anchor the limbs to the axial skeleton. - Pectoral girdle. Part of the skeleton that supports and attaches the upper limbs. The pectoral girdle is formed by the scapula, or shoulder blade, and a clavicle, or collarbone, on both sides of the body. The pectoral girdle connects the bones of the upper limb to the axial skeleton and aids in upper limb movements. - Upper limbs. Each upper limb consists of a humerus, or arm bone, two forearm bones—a radius, and an ulna—and a hand. - The humerus, radius, and ulna articulate with each other at the elbow joint. At the distal end of the radius and ulna is the hand. There are eight carpals, or wrist bones. The five bones of the palm are called metacarpals, and the fourteen bones of the fingers are called phalanges. - Pelvic girdle. The pelvic girdle is formed by two hip bones attached to each other

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anteriorly and to the sacrum posteriorly. The hip bones, the sacrum, and coccyx form the pelvis. Lower limbs. Each lower limb consists of a femur, or thigh bone, two leg bones— a large tibia and a slender fibula—and a foot. The femur and tibia articulate with each other at the knee joint, where the patella, also called the kneecap, covers the anterior surface. At the distal ends of the tibia and fibula is the foot. There are seven tarsals, or ankle bones. The five bones of the instep are called metatarsals, and the fourteen bones of the toes (like the fingers) are called phalanges.

7.6 Skull

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The bones of the cranium are: - Frontal bone. The frontal bone forms the anterior portion of the skull above the eyes. - Parietal bones. One parietal bone is located on each side of the skull just behind the frontal bone. Together, the parietal bones form the bulging sides and roof of the cranium. - Occipital bone. The occipital bone joins the parietal bones along the lambdoid suture. It forms the back of the skull and the base of the cranium. - Temporal bones. A temporal bone on each side of the skull joins the parietal bone along a squamous suture. The temporal bones form parts of the sides and the base of the cranium. - Sphenoid bone. The sphenoid bone is wedged between several other bones in the anterior portion of the cranium. This bone helps form the base of the cranium, the sides of the skull, and the floors and sides of the orbits. - Ethmoid bone. The ethmoid bone is located in front of the sphenoid bone. It consists of two masses, one on each side of the nasal cavity, which are joined horizontally by thin cribriform plates. These plates form part of the roof of the nasal cavity. Facial Skeleton: The facial skeleton consists of thirteen immovable bones and a movable lower jawbone. These bones form the basic shape of the face and provide attachments for muscles that move the jaw and control facial expressions.

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The bones of the facial skeleton are: - Palatine bones. The L-shaped palatine bones are located behind the maxillae. The horizontal portions form the posterior section of the hard palate and the floor of the nasal cavity. - Zygomatic bones. The zygomatic bones form the prominences of the cheeks below and to the sides of the eyes. These bones also help form the lateral walls and the floors of the orbits. - Nasal bones. The nasal bones are long, thin, and nearly rectangular. They lie side by side and are fused at the midline, where they form the bridge of the nose. - Mandible. The mandible, is also called the lower jawbone. It has a horizontal, horseshoe-shaped body with a vertical, flat portion projecting upward at each end. 7.7 Vertebral Column - The vertebral column extends from the skull to the pelvis and forms the vertical axis of the skeleton. It is composed of many bony parts, called vertebrae, that are separated by masses of fibrocartilage called intervertebral discs and are connected to one another by ligaments. The vertebral column supports the head and trunk of the body, and protects the spinal cord. - Cervical Vertebrae: Seven cervical vertebrae compose the bony axis of the neck. - Thoracic Vertebrae: The twelve thoracic vertebrae are larger than the cervical vertebrae. - Lumbar Vertebrae: Five lumbar vertebrae are in the small of the back (loin). - Sacrum: A triangular structure, composed of five fused vertebrae, that forms the base of the vertebral column.

7.8 Thoracic Cage - Includes the ribs, thoracic vertebrae, sternum, and the costal cartilages that attach the ribs to the sternum. - These bones support the pectoral girdle and upper limbs, protect the viscera in the thoracic and upper abdominal cavities, and play a role in breathing. - Ribs: the usual number of ribs is twenty-four--one pair attached to each of the twelve thoracic vertebrae. - Sternum: the breastbone is located along the midline in the anterior portion of the thoracic cage. 7.9 Pectoral Girdle - The shoulder (pectoral) girdle, is composed of four parts--two clavicles and two scapulae. - The pectoral girdle is an incomplete ring.

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It is open in the back between the scapulae, and the sternum separates its bones in front. - Clavicles: the collarbones, are slender, rodlike bones with elongated S shapes. - Scapulae: the shoulder blades are broad, somewhat triangular bones located on either side of the upper back. 7.10 Upper Limbs - The bones of the upper limb form the framework of the arm, forearm, and hand. - They also provide attachments for muscles and interact with muscles to move limb parts. - These bones include: humerus, radius, ulna, metacarpals, and phalanges. - Humerus: a long bone that extends from the scapula to the elbow. - Radius: is located on the thumb side of the forearm, extends from the elbow to the wrist. - It crosses over the ulna when the hand is turned so that the palm faces backward. - Ulna: the ulna is medial to the radius. - It is longer than the radius and overlaps the end of the humerus posteriorly. - Hand: The hand is made up of the wrist, palm, and fingers. - The skeleton of the wrist consists of eight small carpal bones firmly bound in two rows of four bones each. - The resulting compact mass is called a carpus. - The carpus articulates with the radius and with the fibrocartilaginous disc on the ulnar side. Its distal surface articulates with the metacarpal bones. - Five metacarpal bones, one in line with each finger, form the framework of the palm or metacarpus of the hand. These bones are cylindrical, with rounded distal ends that form the knuckles of a clenched fist. They are numbered 1–5, beginning with the metacarpal of the thumb. - The phalanges are the finger bones. Each finger has three phalanges—a proximal, middle, and distal phalanx—except the thumb, which has two (it does not have a middle phalanx). 7.11 Pelvic Girdle Consists of two hip bones (coxal bones, pelvic bones, or innominate bones) that articulate with each other anteriorly and with the sacrum posteriorly. Each hip bone develops from three parts--an ilium, ischium, and pubis. The ilium, which is the largest and uppermost portion of the hip bone, flares outward, forming the prominence of the hip. The ischium, which forms the lowest portion of the hip bone, is L-shaped, with its angle, the ischial tuberosity, pointing posteriorly and downward. The pubis constitutes the anterior portion of the hip bone. 7.12 Lower Limbs Bones of the lower limb form the framework of each thigh, leg, and foot. - They include the femur, tibia, fibula, tarsals, metatarsals, and phalanges. - Femur: the thigh bone--and is the longest bone in the body. It extends from the hip to the knee.

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A patella, or kneecap, also articulates with the femur on its distal anterior surface. - Is located in a tendon that passes anteriorly over the knee. Tibia: the shin bone--the larger of the two leg bones and is located on the medial side. Fibula: a long, slender bone located on the lateral side of the tibia. Foot: the ankle, or tarsus, is composed of seven tarsal bones. - The instep, or metatarsus, consists of five elongated metatarsal bones that articulate with the tarsus. - They are numbered 1-5, beginning on the medial side.

7.13 Joints - Types of Joint Movements:...